Dear M^r. Darwin

I have to offer you my sincere thanks for the copy of your volume on “Vegetable Mould” which has just reached me, and which I shall at once read.¹ Since you wrote to me on the subject of the action of the Earth-worm in 1871 I have watched the operations of the animal with keen interest and have convinced myself of its importance in such a humid country as ours.²

A recent journey through the western territories of N. America has suggested to me that without in any way undervaluing the action of the earth-worm, we are apt to neglect too much the growth of soil by wind-transport.³ The enormous extent of the superficial disintegration of rocks in a dry climate with a daily range of temperature often exceeding 70^o. astonished me and raised in my mind the question whether on a minor scale the same phenomena and the associated denudation & transport by wind might not have more geological importance here than we have supposed.

Yours very truly | Arch Geikie